At-Surface Reflectance and Albedo from Satellite for Operational Calculation of Land Surface Energy Balance Masahiro Tasumi 1 ; Richard G. Allen 2 ; and Ricardo Trezza 3 Abstract: This paper presents a rapid, operational method for estimating at-surface albedo applicable to Landsat and MODIS satellite sensors for typical cloud-free, low-haze conditions and sensor view angles less than 20°. At-surface albedo estimates are required input to various surface energy balance models that are applied operationally. The albedo calculation method was developed using the SMARTS2 radiative transfer model and has been applied in recent versions of the University of Idaho METRIC model as a component of the surface energy balance for determining evapotranspiration. The albedo procedure uses atmospheric correction functions developed to require only general humidity data and a digital elevation model. The atmospheric correction functions have a reduced structure to enhance their operational applicability in routine instantaneous surface energy balances and to estimate evapotranspiration. The method does not require high levels of knowledge in atmospheric physics and radiation transfer processes, common to traditional radiation transfer models, which enhances their use by a broad range of agricultural and hydrologic scientists and engineers. The atmospheric correction and surface albedo estimation procedures are developed primarily for use with Landsat imagery, which does not have an official albedo product. However, the procedure is also applicable to MODIS imagery that has an official albedo product at the 1 km scale, for situations where full broadband albedo having 500 m resolution is needed, where albedo is needed for select days having small sensor view angles for reduction of pixel blurring, or where image striping or reflectance data fallout has occurred in the standard MODIS albedo product. Method results have been compared to literature values and independent data sets. Test applications against MODIS albedo products in New Mexico, Florida, and Idaho indicate that the expected error for actual albedo from the developed method is within the interval of -0.035 to +0.033 95% confidence level, equivalent to a standard error of 0.017, over broad ranges in land surface elevation, humidity, and sun angle. DOI: 10.1061/ASCE1084-0699200813:251 CE Database subject headings: Energy; Satellites; Evapotranspiration; Hydrology. Introduction Landsat has been one of the primary operational earth observation satellites over the past three decades. With long-term historical image records and high spatial resolution of 30 m in the short wave bands and 60– 120 m in the thermal band, Landsat thematic mapper TM and enhanced thematic mapper plus ETM+  im- ages have been widely utilized for both research and nonresearch purposes. The high resolution of Landsat makes this satellite highly valuable for agricultural and water resources management, where reflective and thermal information can be retrieved for in- dividual agricultural fields. On the other hand, the moderate- resolution imaging spectroradiometer MODIS on board the Terra and Aqua satellites is a relatively new, but coarser, sensor, available since 1999. Because MODIS produces highly auto- mated, low-cost images having relatively frequent, albeit coarser coverage than Landsat, MODIS images have become widely used for earth observation at the moderate spatial resolution of 250–1000 m. Solar energy reflected from the earth’s surface, as observed by satellite, is impacted by attenuation and scattering by the atmo- sphere between the satellite sensor and the surface target. The atmospheric effect must be eliminated during calculation of sur- face reflectance and albedo albedo represents the broadband re- flectance over the entire shortwave spectrum and for land surface energy balance computations. Radiation transfer models RTMs are generally accepted for atmospheric correction of reflected ra- diation Staenz et al. 2002. Application of RTM, for example the MODTRAN model Berk et al. 1999, is common in research applications that require high accuracy of at-surface reflectance and integrated albedo. In operational modes of atmospheric cor- rection, the related 6S RTM Vermote et al. 1997 is commonly applied, and is more computationally efficient than MODTRAN e.g., Zhao et al. 2000. However, application of these RTM’s in routine energy balance computations by public water manage- ment agencies, for example, the Idaho Department Water Resources that routinely applies the METRIC satellite-based evapotranspiration ET model Kramber 2002; Allen et al. 2005, 2007a, is not popular for two reasons. First, extensive computa- tional requirements of most RTM’s involve the creation of lookup tables for standard atmospheric conditions to enable quick atmo- spheric correction Liang et al. 2001. Second, ET and energy balance model operators may not have sufficient theoretical back- ground and training to manipulate RTMs, since many operators are hydrologists, engineers, or GIS spatial analysts by training. 1 Associate Professor, University of Miyazaki, 1-1, Gakuen Kibanadai- Nishi, Miyazaki 889-2192, Japan. E-mail: tasumi@cc.miyazaki-u.ac.jp 2 Professor, Kimberly Research Center, University of Idaho, 3793 N 3600 E., Kimberly, ID 83341. E-mail: rallen@kimberly.uidaho.edu 3 Visiting Associate Professor, University of Idaho, 3793 N. 3600 E., Kimberly, ID 83341. E-mail: rtrezza@kimberly.uidaho.edu Note. Discussion open until July 1, 2008. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on May 8, 2006; approved on October 31, 2006. This paper is part of the Journal of Hydrologic Engineering, Vol. 13, No. 2, February 1, 2008. ©ASCE, ISSN 1084-0699/2008/2-51–63/$25.00. JOURNAL OF HYDROLOGIC ENGINEERING © ASCE / FEBRUARY 2008 / 51